It is an old axiom of medicine that pus collections must be drained for healing to occur. Pus that becomes locally trapped under the skin and produces an inflammatory reaction is called an abscess (i.e., furuncle or boil). Carbuncles are aggregates of infected follicles. Cellulitis may precede or occur in conjunction with an abscess. An abscess is not a hollow sphere; it is a cavity formed by fingerlike loculations of granulation tissue and pus that extends outward along planes of least resistance. A paronychia is a localized abscess that involves a nail fold.

Staphylococcus aureus and Streptococcus species are the most common causative agents, but other microorganisms, including gram-negative and anaerobic bacteria, may be present. Enteric organisms are common in perianal abscesses.

Abscesses may follow one of two courses. The abscess may remain deep and slowly reabsorb. Alternatively, the overlying epithelium may attenuate (i.e., pointing), allowing the abscess to spontaneously rupture to the surface and drain. Rarely, deep extension into the subcutaneous tissue may be followed by sloughing and extensive scarring. Conservative therapy for small abscesses includes warm, wet compresses and antistaphylococcal antibiotics. The technique of incision and drainage (I&D) is a time-honored method of draining abscesses. Routine cultures and antibiotics are usually unnecessary if an abscess is properly drained.

After I&D, instruct the patient to watch for signs of cellulitis or recollection of pus. Train patients or family to change packing, or arrange for the patient's packing to be changed as necessary. Cellulitis, bacteremia, and gangrene are rare complications and occur most commonly in patients with diabetes or other diseases that interfere with immune function. I&D of a perianal abscess may result in a chronic anal fistula and may require a fistulectomy by a surgeon

■ An abscess that is not spontaneously resolving

■ Consider more aggressive therapy, closer observation, wound culture, and antibiotic therapy in patients with diabetes, debilitating disease, compromised immunity, or facial abscesses located within the triangle formed by the bridge of the nose and the corners of the mouth. The latter infections carry a risk of septic phlebitis with intracranial extension.

■ Prep and drape the area in a sterile fashion. Administer a field block with local anesthetic. The skin overlying the top of the abscess also is anesthetized.
PITFALL: Avoid injecting into the abscess cavity, because local anesthetics usually work poorly in the acidic milieu of an abscess.

The abscess is ready for drainage when the skin has thinned and the underlying mass becomes soft and fluctuant (i.e., pointing). A no. 11 surgical blade is inserted and drawn parallel to the lines of lesser skin tension, creating an opening from which pus may be expressed. Often, an up-and-down incision with the no. 11 blade is adequate. Avoid extending the incision into non-effaced skin. Apply pressure around the abscess to expel pus from the wound.
Abscesses can explode upward on entry. Wear protective eyewear if the abscess contents appear to be under pressure.

Abscesses most often recur because of an incision that is not wide enough to prevent immediate closure.

Insert a probe, cotton-tipped applicator, hemostats, or curette through the opening, and draw it back and forth to break adhesions and dislodge necrotic tissue. If a culture is desired, obtain it from deep in the abscess cavity.

If the cavity is large enough, pack it with a ribbon of plain or iodoform gauze to promote drainage and prevent premature closure. Grasp the end of the ribbon with a pair of forceps, and place it through the incision to the base on the abscess. Fold additional ribbon into the cavity until it is filled. Leave approximately 1-2 cm of gauze on the surface of the skin. Apply a sterile dressing over the area

(1) Administer a field block with local anesthetic.

(2) Make an up-and-down incision with a no. 11 surgical blade, and apply pressure around the abscess to expel the pus from the wound.

(3) Insert a probe through the opening, and draw it back and forth to break adhesions and dislodge necrotic tissue.

(4) If the cavity is large enough, pack it with plain or iodoform gauze to promote drainage and prevent premature closure.


Treatment of Soft Tissue Infections When Methicillin-Resistant Staphylococcus aureus Is Suspected or Is the Known Pathogen

Severity of Illness Type of Infection Antibiotic
Mild Skin abscess after I & D No antibiotics.* 
Cellulitis or
Clindamycin, 300 milligrams PO three to four times per day for 7-10 d.
Trimethoprim/sulfamethoxazole double strength one to two tablets twice per day PO.
Cephalexin, 500 milligrams PO four times per day for 7-10 d.
Moderate Stable patient with cellulitis or abscess after I & D requiring hospital admission Clindamycin, 600-900 milligrams IV every 8 h.
Worsening infection despite outpatient therapy Vancomycin, 1 gram IV every 12 h.
Linezolid, 600 milligrams IV every 12 h.
Severe NSTI Vancomycin, 1 gram IV every 12 h (or possibly linezolid, 600 milligrams IV every 12 h).
Patient with significant comorbidities
Meropenem, 500-1000 milligrams every 8 h IV.
Piperacillin/tazobactam, 4.5 grams every 6 h, or imipenem-cilastatin, 500 milligrams every 6 h. Consider also addition of clindamycin IV in cases of a NSTI to mitigate toxin production.

■ Bleeding
■ Extension of infection
■ Recurrence

 ■ Drainage of pus indicates correct localization of pus but follow-up must be provided to ensure progression of adequate drainage.